Interatrial block (IAB), denoted by P waves ≥110 ms, is believed to be associated with underlying ischemia, particularly with that of its principal interatrial conduction pathway, the Bachmann bundle. We investigated if there is an angiographic association of IAB on electrocardiograms at rest in patients who underwent cardiac angiography after a positive exercise tolerance test (ETT) result. Twenty-seven patients with IAB and 42 control patients without IAB on electrocardiograms at rest who had evidence of ischemia on cardiac angiography after ETT were identified. Coronary vessels that were angiographically most significantly stenosed (≥70% occlusion indicating stenosis) were noted for statistical comparison (a p value <0.05 was considered statistically significant). Among patients with IAB, the right coronary artery was the predominant vessel to be affected, with ≥70% narrowing compared with the left, inclusive of the left main, left circumflex, obtuse marginal, and diagonal coronary arteries (58% vs 23%, p = 0.03). Right coronary artery lesions in patients with IAB were mostly in the proximal and mid portions (54% vs 25% for the entire left coronary artery, p = 0.02). No such difference was noted in control subjects. In conclusion, in patients with IAB at rest who have coronary heart disease, the right coronary artery is predominantly more significantly affected.